A method of operating a disk drive to efficiently recover from an event which interrupts a safe-to-write condition that occurs during a write operation includes receiving a string of data blocks for writing on respective addressable locations on a track of a disk in the disk drive. During a pass of the addressable locations under the read/write head, the head is positioned to follow the track within a tolerance limit and a first write operation is started to write the string of data blocks on the track. During the first write operation, if it is detected that a safe-to-write condition no longer exists, as may be triggered by a shock event, the first write operation is aborted. When it is later determined that the safe-to-write condition is asserted, a second write operation is defined to write a set of addressable locations within the string of data blocks which have yet to pass under the read/write head and the second write operation is performed. By performing the second write operation as soon as possible, the performance of the drive is improved.
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1. In a disk drive having a head positioned over a track on a rotating disk, a method of writing a string of data blocks having a starting data block and an ending data block which are required to be written sequentially in respective addressable locations disposed on the track, the respective addressable locations having a leading addressable location corresponding to the starting data block and a trailing addressable location corresponding the ending data block and a pass is defined to be an interval which is initiated by the leading addressable location passing under the head, and terminated by the trailing addressable location passing under the head, the method comprising the steps of
determining if the head is positioned within a safe-to-write window; if the bead is determined to be positioned within a safe-to-write window performing the steps of: determining that an addressable location which is required to be written has passed under the head during the pass without being written; determining if another addressable location which is required to be written has yet to pass under the head during the pass; if so then writing to the other addressable location during the pass. 2. The method of
4. The method of
5. The method of
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1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a method of operating a disk drive for writing to an addressable location after detecting that a head is within a safe-to-write window.
2. Description of the Prior Art
A disk drive has a control system generally comprising an interface microprocessor, which directs the activities of the disk drive, and a servo microprocessor, which controls the position of a read/write head. The interface and servo functions may be embodied in a single microprocessor or in separate microprocessors. A disk controller or formatter circuit automates disk data transfer functions such as reading and writing data sectors under control of the interface microprocessor. An exemplary such disk drive is shown in commonly assigned U.S. Pat. No. 5,965,992 to Goretzki et al which is hereby incorporated by reference.
During a write operation initiated by a host computer, a disk drive receives a sequential series or "string" of data blocks from the host. The string of data blocks is stored in a disk memory buffer for writing to corresponding addressable locations on a data track of a disk. Each addressable location may be a structure on the track known as a data sector, conventionally referenced by a logical block address (LBA). The control system of the disk drive requires that the read/write head be positioned over the track and that the head follow the track to within a tolerance limit during the entire write operation. When the head is positioned within the tolerance limit, the head is said to be within a safe-to-write window. If the head wanders off-track or outside the tolerance limit for whatever reason during a write operation, the head is declared to be outside the safe-to-write window by the control system and the write operation must stop to avoid overwriting data on an adjacent track or tracks. One reason the head may wander off-track is that the drive may have been subjected to a shock impulse. Conventionally, to recover from such a shock event, the disk drive control system will wait until the head is once again following the track within the tolerance limits and the first addressable location corresponding to the string passes under the head on a subsequent revolution of the disk before attempting to re-write the string of data blocks. The control system will therefore wait until the appropriate servo wedge preceding the first data block to be written passes under the head to verify track following within tolerance levels before attempting the write operation again.
It should be understood for this discussion that the disk drive head conventionally comprises an integration of separate read/write elements in a fixed relationship such that the read element provides position information to the servo controller and the servo controller uses the position information to position the head to place the write element on track for writing.
A shock event is one such temporary condition. During the shock event, the head may have wandered outside a safe-to-write window, increasing the likelihood that data on adjacent tracks may be inadvertently overwritten. After reading the servo wedge S2 and determining that the head is now back on the desired track or within the tolerance limit, the safe-to-write signal is re-asserted. There is some latency between the reading of the servo wedge S2 and the reassertion of the safe-to-write signal as the head passes over data sector D6, as some processing time is required to determine the position of the head. Although the diagram of
The writing of the data blocks, as shown in the upper portion of
Original Equipment Manufacturers (OEM's) of disk-drive-containing systems often specify disk drive performance requirements that must be met by disk drive manufacturers. Such requirements often specify the maximum data transfer performance degradation that is allowed as the drives are subjected to and recover from an event (such as a shock impulse) that causes a safe-to-write condition to be terminated. In the case of a shock event, such performance requirements may be met by equipping the drive with costly shock sensors or mechanical shock dampeners, for example. Competitive pressures in the disk drive industry, however, preclude such a course of action. A preferred solution to the problem of efficiently recovering from an off-track condition would not require such added hardware. There is a need, therefore, for methods of operating a disk drive to efficiently recover from events terminating a safe-to-write-condition that do not depend upon costly mechanical hardware or added manufacturing steps.
This invention may be regarded as a method for writing a string of data blocks in a disk drive. The disk drive has a head positioned over a track on a rotating disk. The string of data blocks has a starting data block and an ending data block which are required to be written sequentially in respective addressable locations disposed on the track. The respective addressable locations include a leading addressable location corresponding to the starting data block and a trailing addressable location corresponding the ending data block. With regard to the invention, a pass is defined to be an interval which is initiated by the leading addressable location passing under the head, and terminated by the trailing addressable location passing under the head. The method of the invention comprises the steps of determining if the head is positioned within a safe-to-write window and if the head is determined to be positioned within a safe-to-write window, performing the steps of determining that an addressable location which is required to be written has passed under the head during the pass without being written; determining if another addressable location which is required to be written has yet to pass under the head during the pass; and if so then writing to the other addressable location during the pass.
Referring to
Referring to
Thereafter, using the method of the invention, at servo wedge S2 during the first pass, the control system determines that the head is back within the tolerance window for writing. The control system then re-asserts the safe-to-write signal as shown. The method then determines at point 250 for example that the safe-write-signal is asserted and that an addressable location which is required to be written such as any of D3 through D6 has passed under the head without being written. The method then determines that an addressable location, such as D10, which is required to be written has yet to pass under the head during the first pass. The method schedules a disk controller command "Write D1-D12" and after verifying at servo wedge S3 that the safe-to-write signal remains asserted, writes to addressable locations D10-D12.
On a subsequent pass (Second Pass), the control system schedules a disk controller command to write the addressable locations D3-D9 which were not written during the first pass and as a precaution re-writes addressable locations D1-D2 as well. It may be noted that no rotational latency penalty ensues from the rewriting of D1-D2. By observing the summed length of arrowed segments 202 and 204 compared to the corresponding prior art segments in
Moreover, this performance improvement does not necessitate additional hardware or manufacturing steps. The method of the invention is preferably stored in a disk drive magnetic media or in ROM and executed from RAM or ROM by a disk microprocessor such as that shown in the aforementioned commonly assigned patent to Goretzki et al.
Codilian, Raffi, Nazarian, Ara W.
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